Liquid purification or separation – Processes – Including geographic feature
Reexamination Certificate
1999-09-23
2002-08-06
Popovics, Robert (Department: 1723)
Liquid purification or separation
Processes
Including geographic feature
C366S264000, C366S270000
Reexamination Certificate
active
06428711
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a purification method of a closed water area in a bay, a lake, a marsh, a dam lake, etc., in which water is dead and less movable, and to an apparatus for use in the purification.
BACKGROUND OF THE INVENTION
In a closed water area in a bay, a sea water culture has been carried out for a long time. Since the water in a bay is less exchangeable with a water of open sea, the water in a bay is polluted due to self-contamination. Also, in a lake, a marsh and a dam lake, the water is polluted due to inflow and accumulation of domestic waste water. Since the water in a closed water area is less exchangeable as mentioned above, the water is thermally stratified most of a year as shown in FIG.
4
. The stratification of the water in a closed water area occurs due to a density gradient between a surface layer water, a middle layer water and a bottom layer water. The density gradient is caused by a decrease in the density of the surface layer water due to a heat of solar radiation and a temperature difference between the water and air contacting the water surface. The thermal stratification of
FIG. 4
consists of, from the bottom, a bottom layer
52
having a low temperature and a high density, a thermocline layer
53
thereon in which the temperature abruptly changes, and a surface layer
54
having a high temperature and a low density. In addition to the stratification due to the temperature difference, a stratification due to a difference in dissolved oxygen (DO) contents may occur.
The atmospheric temperature and the sunshine intensity changes daily and annually, and the water is stratified depending on the daily change and annual change. In
FIG. 4
, a dashed curve
41
shows a temperature distribution of a surface layer water in the daytime, and a curve
42
shows a temperature distribution in the night. The temperature distribution in the night is nearly the same as a temperature distribution caused by the annual differences in sunshine intensity and the atmospheric temperature. In the temperature distribution curve
42
, the portion
53
in which the temperature changes abruptly is referred to as a primary thermocline layer. A surface layer
54
referred to as a secondary thermocline layer has a higher temperature which changes abruptly, and occurs due to the daily differences in sunshine intensity and the atmospheric temperature.
Since the bottom layer water has a low temperature and the sunlight does not reach the bottom layer, the photosynthesis by phytoplanktons does not take place there and oxygen is not released to the bottom layer. Also, since the stratification prevents the convection of the water, the dissolved oxygen (DO) in the surface layer is not transferred to the bottom layer. Therefore, the bottom layer water forms an oxygen-deficient water mass having a DO content of nearly zero.
Contrary to the bottom layer, since the surface layer has a higher temperature and receives a sufficient amount of sunshine, the photosynthesis by phytoplanktons vigorously occurs therein and oxygen in the air contacting the water surface is also dissolved into the surface layer water, the DO content of the surface layer water reaches 8-10 ppm, in some cases, reaches a supersaturated amount of about 30 ppm.
In the stratifying phase (summer season in which a large temperature difference is created between the surface layer, the middle layer and the bottom layer), the oxygen-deficient water mass on the mud of the sea-bottom or lake-bottom becomes a density current (thin laminar flow) and flows into a recessed or depressed portion of the sea-bottom or lake-bottom and accumulated there. In the recessed portion, organic substances such as dead bodies of phytoplanktons are sedimented and accumulated to form the mud. In the oxygen-deficient water mass having a low DO concentration, anaerobic bacteria actively produce from the mud nutritive salts of organic acids, ammonia, phosphoric acid, etc. and poisonous gases such as hydrogen sulfide to make the oxygen-deficient water mass more eutrophic.
In late summer or autumn (from September to October in Japan) in which the atmospheric temperature sometimes becomes lower than the water temperature, the thermal stratification of the closed water area is gradually disappeared to enter upon a circulating phase. At be beginning of the circulating phase, the oxygen-deficient water mass in the bottom layer occasionally rises near the surface layer by some external causes such as a transitory wind to kill the cultured fishes, etc. in a short time. Also, since the oxygen-deficient water mass is rich in the nutritive salts, the oxygen-deficient water mass rising into the surface layer receiving a strong sunlight causes an explosive growth of phytoplanktons such as water bloom, thereby preventing the good use of the water.
The temperature distributions in the depth direction of the same closed water area (Ohfunato Bay in Iwate-ken, Japan) are shown in
FIG. 5A
for the stratifying phase in summer (August) and in
FIG. 5B
for the circulating phase in late autumn (November).
FIGS. 6A and 6B
schematically show the distribution of the dissolved oxygen concentration in the water depth direction of the same closed water area in the same season as in
FIGS. 5A and 5B
. In summer, both the water temperature and the dissolved oxygen concentration change consecutively from the surface layer to the deep layer to form a stable stratification. However, in late autumn, the stratification is disappeared and the distributions of the water temperature and the dissolved oxygen concentration become unclear. In summer in which the closed water is thermally stratified, the oxygen-deficient water mass having a DO concentration of 4 ppm (mg/liter) is likely to be formed particularly in a recessed portion of the sea-bottom and lake-bottom.
To avoid the damage due to the rise of the oxygen-deficient water mass into the surface layer, proposed is a method for disappearing the oxygen-deficient water mass in the bottom layer, in which the bottom layer water containing the oxygen-deficient water mass is pumped up and discharged into the surface layer to mix the oxygen-deficient water mass with the surface layer water to diffuse the oxygen-deficient water into the oxygen-rich water of the surface layer of the closed water area. In another method, the oxygen-deficient water mass is disappeared by discharging a sucked surface layer water into the bottom layer to mix the surface layer water and the bottom layer water.
As a means for practicing the above method, Japanese Patent Laid-Open No. 5-309395 discloses agitating aeration apparatuses shown in
FIGS. 7 and 8
.
The agitating aeration apparatus of
FIG. 7
comprises a float
101
and a pump
102
vertically suspended from the float
101
. The pump
102
comprises a discharge casing
103
, an intake casing
104
, an electric motor
105
, and an impeller
106
. An opening
103
a
of the discharge casing
103
is positioned in the surface layer water, and an opening
104
a
of the intake casing
104
is positioned in the bottom layer water. Upon rotating the impeller
106
, the bottom layer water is sucked through the opening
104
a
of the intake casing
104
as shown by arrows A, A, and discharged horizontally from the opening
103
a
of the discharge casing
103
in the direction shown by arrows B, B.
The agitating aeration apparatus of
FIG. 8
comprises a float
111
and a pump
112
vertically suspended from the float
111
. The pump
112
comprises an intake casing
113
, a discharge casing
114
, an electric motor
115
, and an impeller
116
. An opening
113
a
of the intake casing
113
is positioned in the surface layer water, and an opening
114
a
of the discharge casing
114
is positioned in the bottom layer water. Upon rotating the impeller
116
, the surface layer water is sucked through the opening
113
a
of the intake casing
113
as shown by arrows C, C, and discharged horizontally from the opening
114
a
of the discharge casing
114
in the direction shown by ar
Kobayashi Katsuya
Nakamura Makoto
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Popovics Robert
Tokyo Kyuei Co., Ltd
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